This invention relates to a storage apparatus, particularly a low-temperature storage apparatus.
It is well known to use liquid nitrogen in the short-term and long-term storage of biological materials such as blood cells and micro-organisms. The storage is meant to preserve the biological integrity of cellular tissues and organisms for future therapeutic use and research.
Liquid nitrogen is used in part because it is has a relatively low boiling point. Owing to difficulties in manufacture, however, liquid nitrogen is a very expensive substance. Consequently, U.S. Pat. No. 5,029,447 described a storage apparatus having several chambers storing specimens at different temperatures. Specimens were moved from chamber to chamber, thereby maintaining viability of the stored specimens even though at any one time only a portion of the specimens were in a chamber at liquid nitrogen termperatures. This design enables the use of coolants other than liquid nitrogen for at least some of the storage chambers, thereby reducing the storage expense.
It has been recognized that different types of biological specimens, namely different tissue types, have different optimum thawing and freezing rates or combinations of rates (protocols). U.S. patent application Ser. No. 670,979 describes a method and system for automatically freezing and thawing specimens which have such different rates or protocols. The system facilitates storage operations, particularly when many specimens are involved.